In the case where the same kind of navigational data is received from different sources, we need to decide which is the main and most trustworthy source. OpenCPN prioritization logic is based on position, Lat/Lon, data. A source or device used for the ship’s position will also, by default, be used for course/speed (COG/SOG), variation and GNSS status, if available.
Several position sources, GNSS receivers, are normally connected to OCPN. For security reasons it’s common to have at least two vailable on board: either two single sensors or one standalone receiver and the receiver in a AIS transceiver. Both can not normally be used simultaneously in OCPN. Also since they are likely not mounted on the same physical position, the ship symbol in OCPN will “jump”, which is more obvious when zoomed in. We need to give priority to one of the two sources and at the same time be sure the lower priority source will be used in the event of malfunction of the first.
These are the basics for the priority list. By default, the first received position source will be the one with priority. This will also set prioritization order for other navigational data mentioned above.
The user can anytime edit the prioritization order. Click button “Adjust communication priorities…”
A quite common collection of NMEA0183 serials to the left and some network and serial NMEA2000 connections to the right. For the left collection no variation source was found. Plugin WMM will be used. The upper source has priority and will be used if available. The source with bold font is the one in use for the moment. If the priority source is temporarily lost, the next source down will be used and marked in bold. As soon the priority source is recovers, that one will again be active and bold.
Position defaults to be “master” of priority. Select the desired source and move it up to the top position by the button “Move up”. In the Nmea0183 example above “nmea0183COM7:0:GPRMC“ is moved to top. This device is newer and more stable and therefore has priority. Now when a position source row is moved to top, corresponding sources for Speed/Course, Variation and Satellites are automatically moved to top. The upper source is always first in the priority list. So, moving a source down on the list will have corresponding effect.
After Position priority is set, study the other and consider the relevance. Now they can be individually changed if desired. If, for example, Variation from one source is known to be “out of date”, select and move another source to the top of the list.
Heading priority is not automatically adjusted when position priority is set. If available, and more than one, you should move up/down the most trustworthyt source on top of the Priority List.
toolbar-options-connections-Prio-list-N2k toolbar-options-connections-Prio-list-RPi Study the position source,s on above pictures. Each row contains three fields: Protocol Port/Address : Source ID ; Message -Protocol is either of available connection types. -Port is a serial RS2323|USB port or a network address:port. (socketCan e.g. can0 is for Linux only) -Source ID is a identifier used when the same message are available from different devices on the same port/address. See the nmea2000 COM7:1/2:129025 above. PGN 129025 is present from two devices on the same N2k bus. They have got unique ID to be able to priority in between. Every device on a N2k bus has a unique ID. (Sadly enough it can vary over time) -Message: Designation for a N0183 message, a N2k PGN or signalK in general.
<Priority scheme is saved to config file> When OCPN is closing the priority table is saved to the config/ini -file. So once a priority order is set up and all connected data sources are stable between OCPN stop-start the priority order will remain and being reused every time.
Move up – Move Down
A selected row in the priority dialog will move up or down. When moved up the priority order will change. The upmost source will always be prioritized if available. If for any reason no data is received from that source the next source in the list will be used instead and marked with a bold font. If the priority source is again receiving relevant data that will again being used. Again, indicated by font in bold.
Refresh
If connections are changed while the list is shown, e.g. one source is down or up again, the Refresh button will reload and update the priority table.
Clear all
As mentioned above the priority table is saved to the config/ini -fil to be reused at next OCPN start. If for any reason, like replacing a connected device with another the priority table may need to be rebuilt. Use the “Clear All” button and the entire priority table will be cleared out. Also in the config/ini -file. After that a Refresh or a reload of the dialog is needed. It’s recommended to close the priority dialog and wait a minute or two to let all sources be used. Then reopen the dialog and set the new priority list order as desired.
The inbound plugin Dashboard has no own priority list although OpenCPN priority has a direct impact on some instruments. All navigational data in OCPN priority table, Position, course/speed (COG/SOG), satellites and heading are also used by Dashboard. For example, the GNSS Status graph shows data from the same satellite source as in use at the OCPN priority list.
For other instruments where data is not used by OCPN itself, Dashboard Plugin has its own inbound priority logic. If the same data, e.g. true wind or depth, are received from several sources, Dashboard Plugin prioritizes in the following order: